Field Crop 2024, Vol.7, No.2, 70-78 http://cropscipublisher.com/index.php/fc 75 The study by Soumare et al. (2021) emphasizes that PGPR enhances plant growth and increases plant resistance to pests and diseases through mechanisms such as nitrogen fixation, phosphate solubilization, and the production of plant hormones. Meanwhile, AMF enhance plant nutrient uptake efficiency, such as phosphorus, by expanding the root absorption area and improving plant stress tolerance. The illustration shows the different sites and mechanisms of action of PGPR and AMF in the roots and soil, demonstrating their synergistic effects, which significantly improve nutrient utilization, soil health, and yield in rice. This combined application not only optimizes resource use but also sustainably enhances agricultural productivity. 4.2 Comparative studies Comparative studies have consistently shown that PGPM-treated rice fields outperform untreated fields in terms of growth, yield, and nutrient uptake. For example, a study comparing PGPM-treated and untreated rice fields found that PGPM-treated fields had significantly higher dry weight, grain yield, and nutrient uptake, particularly when co-inoculation methods were used (Bakhshandeh et al., 2020). Another study highlighted the superior performance of PGPM-treated fields in terms of micronutrient enrichment and enzyme activity, leading to better overall plant health and productivity (Adak et al., 2016). A meta-analysis of multiple studies on the application of PGPM in rice cultivation reveals consistent positive outcomes. The use of PGPMs, such as Pantoea ananatis, Piriformospora indica, and Anabaena-based biofilm inoculants, has been shown to enhance rice growth, yield, and nutrient uptake across different regions and cultivation practices (Adak et al., 2016; Bakhshandeh et al., 2017; 2020; Chen et al., 2023). The combined application of PGPR and AMF has also been effective in improving soil fertility and rice production, further supporting the potential of PGPMs as biofertilizers in sustainable agriculture . In summary, the application of PGPMs in rice cultivation has demonstrated significant benefits in terms of growth, yield, and nutrient uptake. Comparative studies and meta-analyses confirm the efficacy of PGPMs in enhancing rice productivity, making them a valuable tool for sustainable agriculture. 5 Challenges and Limitations 5.1 Variability in PGPM performance One of the primary challenges in utilizing plant growth-promoting microorganisms (PGPM) is the variability in their performance under different environmental conditions. The effectiveness of PGPM can be influenced by several factors, including soil type, nutrient availability, and climatic conditions. For instance, the study by Bakhshandeh et al. (2017) demonstrated that the co-inoculation of Pantoea ananatis and Piriformospora indica significantly improved rice growth and yield, but the results varied depending on the levels of potassium sulfate fertilizer used. Similarly, Wang et al., (2023) highlighted that the co-inoculant Bacillus velezensis FH-1 and Brevundimonas diminuta NYM3 promoted rice growth by regulating the rhizosphere microbiome, but the extent of this promotion was influenced by the specific soil conditions. These findings underscore the need for site-specific assessments to optimize the use of PGPM in different agricultural settings (Figure 3). Soumare et al. (2021) compared the applications of traditional micropropagation processes and bio-enhanced processes in plant tissue culture. In the traditional micropropagation process, plant explants undergo elongation and proliferation, relying on plant growth regulators such as auxins and cytokinins for rooting and acclimatization stages, before being transplanted into the field. However, this method has a problem with low survival rates. In contrast, the bio-enhanced process introduces beneficial microbes, such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR), which play an important role during the plant elongation, proliferation, and rooting stages. Plants bio-enhanced in this way exhibit better growth during the acclimatization stage and significantly improved survival rates after transplantation to the field.
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